Azeotropic distillation of chloroethyl benzene from chlorostyrene



Patented May 25, 1948 AZEOTROPIC DISTILLATION F CHLORO- ETHYL BENZENEFROM CHLOROSTYRENE Lloyd Berg, OHara Township, Allegheny County,

and James M. Harrison, Oakmont, Pa., assignors to Gulf Research &Development Company, Pittsburgh, Pa., a corporation of Delaware NoDrawing. Application December 17, 1945,

Serial No. 635,602

13 Claims.

This invention relates to azeotropic distillation, and more particularlyto the separation of chlorostyrene from chloroethylbenzene by theaddition of an entrainerto form an azeotropic system which is thendistilled. increasing the amount of highly purified chloro The searchfor plastics suitable for use in synstyrene in the overhead distillateafter the chlorothetic rubber formulation led to theinvestigaethylbenzene azeotrope hasbeen separated. A tion ofchlorostyrene as a substitute for and an chaser is an inert high-boilingliquid whichhas improvement over styrene in the butadiene-stya boilingpoint considerably greater than either rene type of synthetic rubber.However, one of of the compounds to be separated. Suitable the problemsarising in chlorostyrene producchasers are n-cetane and tetradecane.tion is its separation in a high degree of purity We have found a groupof organic compounds from its precursor, chloroethylbenzene. The thatare particularly suitable as entrainers ior' ordinary distillation of achloroethylbenzeneforming azeotropes in accordance with thisinchlorostyrene mixture does not produce a satisvention. These compoundshave the following factory separation in that a low yield ofchlorocharacteristics: styrene of the desired high purity is obtained.(1) The compounds are polar, oxygen-con- This is to be expected in viewof the proximity taining organic compounds. of the boiling points of thecompounds. (2) The boiling points of the compounds lie It is an objectof this invention, therefore, ZO betWeen 55 C. and 76 C. at 10 mm. Hgpressure. to separate, by distillation, monomeric chloro- (3) Thecompounds are miscible with chlorostyrene in a high degree of purityfrom mixtures styrene and chloroethylbenzene. containingchloroethylbenzene and chlorostyrene. (4) The compounds are chemicallyinert with It is a further object of this invention to prerespect tochlorostyrene and chloroethylbenzene. vent the polymerization ofchlorostyrene in the Examples of such polar, organicoxygen-condistillation of mixtures of chlorostyrene and chlotainingcompounds are glycol mono butyl ether, r0ethylbenzene methylacetoacetate, n-hexanol, furfuryl alcohol,

These and other objects are achieved by the tetrahydrofurfuryl alcohol,butyric acid, diacepresent invention, wherein an entrainer which tonealcohol, acetonyl acetone, 2-ethyl butanol, is a chemically inert,polar, organic oxygen-con- 80 diethylaminoethanol, b n hyde, methyl amytaining compound miscible with chlorostyrene carbinol, and 2-am 0- et yD P and chloroethylbenzene and having a boiling In separatingchlorostyrene from chloroethylpoint between 55 C. and 76 C. at 10 mm. Hgbenzene in accordance with this invention, thepressure is added to amixture containing ehloroamount of entrainer added to the charge to beethylbenzene and chlorostyrene to form an azeodistilled is pre yadjusted 50 as t e ptrope with the chloroethylbenzene, and thereproximately equal to the amount required to form suiting mixture isthen distilled to remove the an azeotrope with substantially all of thechloroazeotrope, thereby leaving chlorostyrene substanethylbenzene. Lessthan this amount will-result tially free from chloroethylbenzene. in anincomplete separation of chloroethylben- The azeotrope formed by theentrainer and 40 zene. More than this amount will result in achloroethylbenzene has a lower boiling point than lower yield ofsubstantially pure chlorostyrene any of the other components of thecharge to be in the bottoms stream. However, it should be distilled.Therefore, on distillation, the chlorounderstood that this invention isnot limited to ethylbenzene azeotrope will be separated first, anyspecific amount of entrainer. While the adleaving the chlorostyrenesubstantially free from dition of an amount of entrainer approximatelychloroethylbenzene. equal to the amount required to form an azeo- In,order to avoid the tendency of the chlorotrope with substantially all ofthe chloroethylstyrene to polymerize, the following measures benzene ispreferred, variations of this amount have been found effective, eithersingly or in will nevertheless result in much greater yieldscombination. First, approximately 1 to 2 per of substantially purechlorostyrene. than can be cent of a polymerization inhibitor may beadded obtained by the straight rectification of chloroto the charge tobe distilled. Second, it is adethylbenzene-chlorostyrene mixtures.vantageous to prevent the temperature of the In order to determine thepreferred amount boiling charge from exceeding 100 C., and thereofentrainer to add to the charge to be distilled, it is necessary todetermine the amount of fore the distillation may be conducted at areduced pressure. Third, a high-boiling chaser may be added to thecharge. The addition of a high-boiling chaser has the eflect not only ofreducing the formation of, polymer, but also of sure.

. 3 chloroethylbenzene in such charge. It is also necessary to determinethe. ratio of entrainer to. chloroethylbenzene in the azeotrope formedby theentrainer' and the chloroethylbenzene. From these two factors, theamount of entrainer, to addto any mixture of chloroethylbenzene andchlorostyrene from which it is desired to separate the latter insubstantially pure form may readily be calculated.

The amount of chloroethylbenzene in admixture with chlorostyrene may bedetermined in any convenient manner known to the art, such as bydetermining the refractive index of the unknown mixture and finding the.composition corresponding to such refractive index from a refractiveindex-composition diagram constructed from data on mixtures of knowncomposition.

In determining the ratio of entrainer to chloroethylbenzene in theazeotrope formed by the entrairier'and the chloroethylbenzene, advantageis-taken of the factthat the entrainers 'of this position correspondingto such refractive index from a refractive index-composition diagramconstructed from data on mixtures of known composition. The boilingpoint of the azeotrope and its composition will vary according to thepressure at which such boiling point is determined. However, at anyspecified pressure, the boiling point and composition of the azeotropeare constant. The ratio of entrainer to chloroethylbenzene in theazeotrope is readily calculated after the composition of the azeotropehas been determined. p I

The product of (a) the ratio of entrainer to chloroethylbenzene in theazeotrope, and (b) the amount of chloroethylbenzene in admixture withchlorostyrene in the charge to be distilled, gives the amount ofentrainer to add to the charge. When the amount of entrainer socalculated is added to the charge, upon distillation, an azeotrope isformed with all of the chloroethylbenzene which is distilled over first,and

. substantially pure chlorostyrene is left in the the subsequentdistillation of the entrainer,

chloroethylbenzene, chlorostyrene mixture, provided that the entrainerselected will form an azeotrope with chloroethylbenzene at such pres-Therefore, for the distillation, an entrainer is selected which willform an azeotrope with chloroethylbenzene at the desired pressure.

' A representative range of pressures for the prac-'- tice of thisinvention is from about mm. Hg to about 100 mm. Hg.

The following table shows the azeotropic data for some of the entrainersof this invention;

' Azeotropic data for entrainers Boiling Point Azeotrope with ChloroolEntrainer, ethylbenzeno at 10 "C. mm.

Entrainer Boiling Wt. Per Cent Point, of Chloro- C. ethylbenzene Glycolmonohutyl ether 171. 0 68. 5 62. 5 63. 0 Methyl Amyl Oarbmoln 160. 4 65.4 61. 4 57.0 Methyl Aceto-aoetate 171. 7 65.4 M. 0 48.0 n-Hexanol 157. 065. 0 62. 0 57. 0 Furl'uryl Alcohol 169. 5 71. 0 60. 5 68.0Tetrahydroiuriuryl alcohol. 177. 0 72. l 63. 0 70. 5 Bu yrlc' Acid 163.7 67. 2 63. 3 66.0 Diacetone A 167. 9 61.6 59.0 42.0 Benzaldehyde 179. 065. 0 63. 5 43. 0 Dlethylamlno-ethanol 162. 0 58. 5 57.0 9.0 AcetonylAcetone 191. 4 75. 4 66. 0 76. 0

2-Amino-2-Me'thyl Propanol-l 165. 4 59. 0 54. 0 2-Ethylbutanol 148. 955. 6 54. 9 26. 0

The chloroethylbenzene with which the above data were determined was amixture 01 isomers containing about 8.8 per cent of the ortho isomer,

45per cent of the meta isomer, and46.2 per cent ofth'e para isomer, themixture having a boiling pointof 675 C. at 10 mm. Hg pressure. However,this invention is not limited to any specific combination of isomers,since the separation of chloroethylbenzene from chlorostyrene inaccordance with this invention is applicable to any isomer ofchloroethylbenzene and to any mixture ofsuch isomers. As will beapparent to one skilled in the art, the azeotropic data for any originalazeotrope.

specific isomer or combination of isomers may vary from the data setforth above because oi the variation in boiling point of the differentisomers and their various combinations.

A desirable feature of an entrainer is its ready separability from theazeotropic mix re, after the. azeotrope has been separated .rom thechlorostyrene. Separation, of the entrainer from its azeotrope withchloroethylbenzene permits the reuse of the latter to produce morechlorostyrene and the reuse of the entrainer to produce more azeotrope.Glycol mono butyl ether, furfuryl alcohol, tetrahydrofurfuryl alcohol,butyric acid, diacetone alcohol, methyl acetoacetate, acetonyl acetone,2-amino-2-methyl propanol-l and diethylaminoethanol are sufllcientlywater soluble to permit their separation from their azeotropes withchloroethylbenzene simply by extracting with water. The entrainer may berecovered from the water extract by distillation at a pressure at whichthe entrainer forms no azeotrope with water.

Alternatively, regardless of the solubility of the entrainer in water,separation of the entrainer from its azeotrope with chloroethylbenzenemay be efiected by a. two step distillation as follows: First, theazeotrope from the original distillation is distilled at a pressurediflerent from the original distillation and adapted to yield a bottomsstream of pure chloroethylbenzene and an overhead stream of an azeotropeof entrainer and chloroethylbenzene in which theentrainerchloroethylbenzene ratio is higher than in the For example, ifthe original distillation has been conducted at a reduced pressure toavoid polymerization of the chlorostyrene,

an overhead stream of an azeotrope of chloroethylbenzene and entrainerwhich has a lower entrainer-chloroethylbenzene ratio than themotrope'formed in the first distillation. For, example, if atmosphericpressurehas been used for the flrst distillation, the seconddistillation may be conducted at a reduced pressure. The pure entraineris recycled for use in the o'riginal distillation for separation ofchlorostyrene, and the chloroethylbenzene-rich azeotrope is recycled tothe first distillation.

As another alternative; the original azeotrope of entrainer andchloroethylbenzene may be distilled at a pressure sufliciently high sothat the entrainer no longer forms an azeotrope with thechloroethylbenzene, thus obviating the necessity for a seconddistillation.

The choice of any specific method of recovering entrainer andchloroethylbenzene in practice will depend upon economic considerations.In general, it has been found that the second alternative methoddescribed above is more economical and for that reason is moredesirable.

The following examples further illustrate the invention. Unlessotherwise specifically stated, all parts are by weight,

Example 1.-A mixture of chloroethylbenzene and chlorostyrene was foundto contain 100 parts of the former and 150 parts of the latter. Based onthe amount of chloroethylbenzene present, 56 parts of butyric acid .wereadded which, upon distillation of the mixture at mm. Hg pressure, formedan azeotrope with all of the chloroethylbenzene. The mixture wasfractionated in a rectifying column at 10 mm. Hg pressure. Theazeotropic mixture of chloroethylbenzene and butyric acid distilled overfirst, leaving substantially pure chlorostyrene as the residue. Uponfurther distillation at the same pressure 225 per cent of the originalchlorostyrene in a purity of 95 per cent or higher was obtained in theoverhead distillate and 47 per cent remained in the residue. The totalamount of chlorostyrene recovered in a purity of 95 per cent or higherwas 69.5 per cent. Butyric acid was recovered from itschloroethylbenzene azcotrope by the second alternative meth- 0ddisclosed above. The first distillation was conducted at atmosphericpressure, and the second distillation at 10 mm. Hg pressure.

Example 2.A mixture of chloroethylbenzene and chlorostyrene was found tocontain 41.5 parts of the former and 114 parts of the latter. Based onthe amount of chloroethylbenzene, 58 parts of diacetone alcohol wereadded. Upon distillation of the mixture at 10 mm. Hg pressure, diacetonealcohol in this amount will form an azeotrope with all of thechloroethylbenzene in the mixture. 77 parts of n-cetane were added as ahigh-boiling chaser. The mixture was fractionated in a rectifying columnat 10 mm. Hg pressure. The azeotropic mixture of diacetone alcohol andchloroethylbenzene distilled over first, leaving chlorostyrene behind.Subsequent distillation at the same pressure yielded 62 per cent of theoriginal chlorostyrene in a purity of 95 per cent or higher in theoverhead distillate, and 20 per cent chlorostyrene of the same purity inthe residue. The total substantially pure chlorostyrene recovered was 82per cent. The high-boiling chaser, n-cetane, had the effect of drivingoff most of the chlorostyrene and of reducing the formation of polymerin the residue remaining in the still.

Example 3.To a mixture of 100 parts of chloroethylbenzene and 181 partsof chloro- 3 I styrene, there were added 75 parts of butyl Cellosolve,and 100 parts oi n-cetane as a high-boiling chaser. The mixture wasfractionated in a rectifying column at 10mm. Hg. pressure. The

- azeotropic mixture of chloroethylbenzene and butyl Cellosolvedistilled over first, leaving greater.

chlorostyrene substantially free from chloroethylbenzene. Furtherdistillation at the same pressure yielded 27.5 per cent of the originalchlorostyrene in a purity of 95 per cent or higher in the overheaddistillate and 29.5 per cent chlorostyrene of the same purity in theresidue. The total substantially pure chlorostyrene recovered was 57 percent.

Example 4.-To. a mixture comprising 140 parts of chloroethylbenzene and200 parts of chlorostyrene, there were added parts of tetrahydrofurfurylalcohol. The mixture was fractionated in a rectifying column at 10 mm.Hg pressure. The azeotropic mixture of chloroethylbenzene andtetrahydrofurfuryl alcohol distilled over first, leaving thechlorostyrene substantially free from chloroethylbenzene. Substantiallypure chlorostyrene was recovered in the amount of 65.8 per cent of theoriginal chlorostyrene. Tetrahydrofurfuryl alcohol was recovered fromits azeotrope with chloroethylbenzene by extracting the azeotrope withwater, and distilling the tetrahydrofurfuryl alcohol from the waterextract at atmospheric pressure.

While the above examples show a batch process for the distillation, theadvantages of an azeotropic distillation in accordance with thisinvention are applicable also to a continuous process. No special typeof apparatus is required,

-the conventional batch or continuous stills being satisfactory.

For the purpose of comparing the azeotropic separation of chlorostyrenefrom chloroethylbenzene with the ordinary distillation of mixtures ofthese compounds, the following runs were made. A batch containing 160parts of chloroethylbenzene and 240 parts of chlorostyrene werefractionated in a rectifying column at 10 mm. Hg pressure. Only 35 percent of the original chlorostyrene was recovered from the residue withan apparent purity of per cent or Since the viscosity of the residue hadincreased considerably, the separation was probably enhanced bypolymerization of the chlorostyrene, so that the value of 35 per centmay be considered a maximum. In an eifort to eliminate the formation ofpolymer and to obtain substantially pure monomeric chlorostyrene in theoverhead distillate, another batch containing 160 parts ofchloroethylbenzene, 240 parts of chlorostyrene, 3 parts of2,4-dichloro-6-nitrophenol as polymerization inhibitor, and parts ofncetane as a high boiling chaser were fractionated ina rectifying columnat 10 mm. Hg pressure.

Only 8.8 per cent of substantially pure chloro.

styrene was obtained in the overhead distillate and 5.5 per centremained in the residue in the still. The amount of substantially purechlorostyrene separated was thus only. 14.3 per cent. A comparison ofthe above runs with the examples of this invention shows the outstandingimprovement obtained by the method of this invention over a straightrectification.

As has been shown, the use of high-boiling chasers,- such as n-cetaneand tetradecane, in accordance with this invention, permits recovery ofpure chlorostyrene in the overhead distillate after all of the azeotropehas been distilled over. Furthermore, the chasers also reduce thetendency of the chlorostyrene to polymerizein the still. The-use ofchasers has the effect. therefore, of increasing the yield of puremonomeric chlorostyrene. The amount of chaser to add to the charge to bedistilled is not critical. Approximately 1 part of chaser to 2 to 4parts of chlorostyrene, chloroethylbenzene mixture may be used. Theaddition of approximately 1 to 2 percent of a polymerization inhibitor.to the charge to be distilled also reduces the tendency of thechlorostyrene to polymerize. The use of 2,4-dichloro-6-nitrophenol forthis purpose is preferred.

From the foregoing description, it is apparent that the azeotropicseparationof this invention has many advantages over the straightrectification ofchlorostyrene and chloroethylbenzene mixtures. For anygiven distilling column, using either a batch or continuous process ofdistillation, the separation of chlorostyrene from chloroethylbenzene inaccordance with this invention always results in the recovery of agreater amount of purer chlorostyrene than can be obtained by straightrectification. Furthermore, compared with a straight rectification, anazeotropic separation will reduce the number of theoretical platesrequired in the distilling column; that is, the height of the columnand/or the re.- iiux ratio are not as great as required for a straightrectification. vThe ready separability of the entrainers of thisinvention from their azeotropes with chloroethylbenzene has theadvantage of permitting recovery and reuse of both chloroethylbenzeneand entrainer.

The chloroethylbenzene and chlorostyrene referred to herein have thechlorine substituted in the ring. Accordingly, the termchloroethylbenzene refers to any of the ortho, meta or para isomers, orto mixtures thereof; and, the term chlorstyrene" refers to any of theortho, meta or para isomers or to mixtures thereof. This invention isapplicable to any mixture of chloroethylbenzene and chlorostyrenecontaining any combination of such isomers.

What we claim is:

1. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding to a mixture of said chlorostyrene andchloroethylbenzene a member of the group consisting of glycol mono butylether, methyl amyl carbinol, n-hexanol, iurfuryl alcohol,tetrahydrofurfuryl alcohol, diacetone alcohol, 2-ethylbutanol, 2-amino2- methyl-l-propanol, and diethylaminoethanol to form an azeotrope withthe chloroethylbenzene and then distilling the resultant mixture toremove the azeotrope thereby leaving chlorostyrene substantially freefrom chloroethylbenzene.

2. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding to a mixture of said chlorostyrene andchloroethylbenzenea member of the group consisting of glycol mono butylether, methyl amyl carbinol, n-hexanol. furfuryl alcohol,tetrahydrofurfuryl alcohol, diacetone alcohol, 2-ethylbutanol, 2-amino-Z-methyl-l-propanol, and diethylaminoethanol in amount approximatelyequal to the amount required to form an azeotrope with thechloroethylbenzene and then distilling the resultant mixture to removethe azeotrope thereby leaving chlorostyrene substantially tree iromchloroethylbenzene.

3. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene zene, distilling the resultant mixture at apressure of from 5 mm. Hg to about 100 mm. Hg to remove the azeotropethereby leaving chloro-,

styrene substantially free from chloroethylbenzene and furtherdistilling to recover substantially pure chlorostyrene as distillate.

4. The process of separating chlorostyrene inwhich the chlorine issubstituted in the benzene ring from mixtures thereof with chloroethylbenzene in which the chlorine is substituted in the benzene'ring whichcomprises adding to a mixture of said chlorostyrene andchloroethylbenzene a polymerization inhibitor and a member of the groupconsisting of glycol mono butyl ether, methyl amyl carbinol, n-hexanol,furfuryl alcohol, tetrahydrofurfuryl alcohol, diacetone alcohol,2-ethylbutan0l, propanol, and diethylaminoethanol to form an azeotropewith the chloroethylbenzene and thendistilling the resultant mixture toremove the azeotrope thereby leaving chlorostyrene substan-- tially freefrom chloroethylbenzene.

5. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding to a mixture of said chlorostyrene andchloroethylbenzene an inert liquid having a boiling point higher thanchlorostyrene and chloroethylbenzene and a member of the group,consisting of glycol mono butyl ether, methyl amyl carbinol,

n-hexanol, furfuryl alcohol, tetrahydrofurfuryl' alcohol, diacetonealcohol, Z-ethylbutanol, 2- amino-Z-methyl-l-propanol, anddiethylaminoethanol to form an azeotrope with the chloroethylbenzene andthen distilling the resultant mixture to remove the azeotrope therebyleaving chlorostyrene substantially free from chloroethylbenzene.

6. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding glycol mono butyl ether to a mixture of saidchlorostyrene and chloroethylbenzene to form an azeotrope with thechloroethylbenzene and then distilling the resultant mixture to removethe azeotrope thereby leaving chlorostyrene substantially free fromchloroethylbenzene.

7. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding tetrahydrofurfuryl alcohol to a mixture ofsaid chlorostyrene and chloroethylbenzene to form an azeotrope with thechloroethylbenzene and then distilling the resultant mixture to removethe azeo- 2-amino-2-methyl-1- trope thereby leaving chlorostyrenesubstantially,

free from chloroethylbenzene.

8. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding diacetone alcohol to a mixture of saidchlorostyrene and chloroethylbenzene to form an azeotrope with thechloroethylbenzene and then distilling the resultant mixture to removethe azeotrope thereby leaving chlorostyrene substantially free fromcholorethylbenzene.

9. The process of separating chlorostyrene inwhich the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding glycol mono butyl ether and an inert highboiling liquid having a boiling point higher than the saidchloroethylbenzene and chlorostyrene to a mixture of said chlorostyreneand chloroethylbenzene, distilling the resultant mixture to remove theazeotrope thereby leaving chlorostyrene substantially free fromchloroethylbenzene and then sub-, jecting the undistiiled residue tofurther distillation to separate chlorostyrene therefrom.

10. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtures thereof withchloroethylbenzene in which the chlorine is substituted in the benzenering which comprises adding tetra hydrofurfuryl alcohol and an inerthigh'boiling liquid having a boiling point higher than the saidchlorostyrene or chloroethylbenzene to a mixture of said chlorostyreneand chloroethylbenzene, distilling the resultant mixture to re. "ove theazeotrope thereby leaving chlorostyrene substantially free fromchloroethylbenzene and then subjecting the undistiiled residue tofurther distillation to separate chlorostyrene therefrom.

11. The process of separating chlorostyrene in which the chlorine issubstituted in the benzene ring from mixtura thereof withchloroethylbenzene in which the chlorine is. substituted in of saidchlorostyrene and chloroethylbenzene, distilling the resultant mixtureto remove the azeotrope thereby leaving chlorostyrene substantially freefrom chloroethylbenzene and then subjecting the undistiiled residue tofurther distillation to separate chlorostyrene therefrom.

12. The process of separating chlorostyrene in which the chlorineissubstituted in the benzene ring from a mixture thereof withchloroethylbenzene in which the chlorine issubstituted in thebenzenering which comprises, adding to a mixture of said chlorostyreneand chloroethylbenzene an entrainer selected from the group consistingof glycol mono butyl ether, methyl amyl carbinol, n-hexanol, furfurylalcohol, tetrahydrofurfuryl alcohol, diacetone alcohol, 2-ethylbutanol,2- amino-2-methyl-l-propanol, and diethylaminoethanol to form anazeotrope with the chloroethylbenzene, distilling the resultant mixtureto remove the azeotrope and leave the chlorostyrene substantially freefrom chloroethylbenzene and then distilling the azeotrope at a higherpressure than the pressure at which said azeotrope was styrenesubstantially free from chloroethylbenzene, extracting the azeotropethus formed with water and distilling the water extract to recoversubstantially pure entrainer.

LLOYD BERG.

JAMES M. HARRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES International Critical Tables,vol. 3, pages 319 and 321. (Copy in Scientific Library.)

Lecat, Annelles dds Societe Scientifique de Bruxelles, vol. 49, part 2,pages 291, 292, 3133.

(Copy in Library of U. S. Geological Survey,

Washington, D. C.)

